Hi,
Had exactly the same issue! IS could not connect to the central user management database of MWS.
In my server.log the following error was logged:
[ISS.0024.0001E] Could not initialize User Manager.
I used to have a connection from IS 7.1.2. to my database using the Oracle JDBC drivers (ojdbc14.jar). Everything worked except Central User Managment.
When changing the connection to the DataDirect drivers it finally worked.
Regards